An offshore wind farm at the center of a LIPA plan to address spiking electric demand on the South Fork will produce excess energy when it’s needed least, and fall short of a sharply expanding summer peak load, a recent analysis found.

In a response to questions from Newsday, James Manwell, director of the Wind Energy Center at the University of Massachusetts, found that while effective in helping offset a portion of soaring peak demand – when conventional energy is most expensive – the planned wind farm will be least productive during the peak summer months, when visitors flood the South Fork and additional power is needed most.

“In general, for sure in the Northeast, the winds tend to be higher in winter than in summer,” Manwell said, while “the loads go way up in summer. That’s a bit of a mismatch for sure.”

The project’s 15 turbines will be able to produce a maximum of 90 megawatts of energy, but because the wind doesn’t blow all the time, Manwell estimated that the average actual capacity will be just under half that amount. A megawatt of offshore wind energy powers about 360 homes. Developer Deepwater Wind says the array will provide energy for up to 50,000 homes.

The state comptroller’s office recently reported that Long Island customers will pay $1.62 billion over 20 years to buy all the emission-free energy the array produces. The cost for energy from the project would average about 22 cents a kilowatt hour over 20 years, around three times that of conventional energy.

Manwell called the notion of using offshore wind to address peak power needs an “interesting idea.”

“One normally wouldn’t think of it as such,” because “you just can’t turn on the wind turbine as you would a gas-powered” plant. “Note that most of the load is in the summer,” Manwell wrote in a summary of his findings. “Wind speeds are lower in the summer than other months, but still high enough to result in significant generation.”

In general, Manwell found, 90 percent of the power generated by the wind farm would be used to reduce the annual electrical demand on the South Fork. He noted the turbines would have “some additional benefit” of addressing the summer peak by varying amounts. The increasing summer peak is the reason PSEG Long Island sought bids for new power sources on the East End.

Most days, the South Fork uses about 88.5 megawatts of energy. But in the summer, it more than doubles to 190, according to the report. When that happens, the wind farm will be able to reduce the peak by just about half.

Manwell used a computer model that matched wind speeds in the area off Rhode Island, between Block Island and Martha’s Vineyard, where the wind farm will be constructed. His program looked at each hour of the year, calculated the wind turbine generation and compared it with the electrical demand.

PSEG in response to Newsday questions acknowledged it used “similar techniques” to Manwell’s but “different tools during its development of the South Fork solution.”

“The two analyses measured different sets of parameters, some of which overlap,” PSEG said. “Where there is measurement of similar parameters, the results produced in the [Manwell] report are generally consistent with the results of our analysis.”

PSEG noted, however, that Manwell’s report did not include the impact of energy storage, steps to reduce consumption and transmission enhancements. “One would expect the integration of these technologies into the solution to increase the percentage utilization of energy on the South Fork.”

For its part, project developer Deepwater Wind said that while it agreed with Manwell’s overall findings that appear to show the wind farm’s output “generally aligns with [electric demand] on the South Fork,” it took exception with some conclusions.

Deepwater noted that Manwell’s study used slightly less powerful turbines, but more of them, to reach the 90-megawatt total, and noted the total annual output he projected was about 10,000 megawatt hours less than its own projections.

Deepwater agreed with Manwell’s finding that the array “is expected to produce a significant portion of the South Fork’s energy needs, including during peak demand period.”

As for the cost, Deepwater said, “The appropriate comparable cost is that of building a new fossil-fired generator on the South Fork, where it’s very difficult and expensive to build anything, or a solar renewable energy facility elsewhere on Long Island. . . . Our cost is competitive with that of each of those.”

PSEG and Deepwater noted that other technologies, including large batteries to store excess energy from the array and remote-controlled thermostats to help lower summer electrical demand at Hamptons customers’ homes, will be also be used on the South Fork to moderate the peaks, and store the power for later peak periods.

Moreover, PSEG will simultaneously solve the South Fork peak demand problem with a $513 million series of power cables and upgrades that will cost all LIPA ratepayers about $2.48 a month. LIPA projects the wind farm and other technologies will cost about $1.19 a month when completed in 2022.

Robert Amundsen, an energy-management expert at the New York Institute of Technology in Old Westbury, said LIPA’s plan to use wind energy to address a growing peak need raises questions.

“From an operation standpoint it doesn’t really make sense to consider a wind farm as a peaking resource because the idea of peak is to have the power when you need it, and turn it off when you don’t,” he said. “The wind farm is not like that. That’s not to say it’s not a great idea. But it doesn’t by itself solve your peak power problems. You need to have either enough power in the area or to import it from somewhere else.”

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